Preparation and purification of hydroxylamine stabilizers

ABSTRACT

The invention relates to the preparation of ultra-high purity 1,2-diaminocyclohexane-tetraacetic acid being essentially free of unwanted metal and metal ion contaminants and its use as a stabilizer for ultra-high purity hydroxylamine compounds used extensively in the production of high premium electronic components.

FIELD OF THE INVENTION

The present invention relates to a process for the preparation ofultrapure 1,2-diaminocycloalkyl-N,N,N′,N′-tetraacetic acid (CDTA)compounds and their use as stabilizers for hydroxylamine compositions.

DESCRIPTION OF THE PRIOR ART

Hydroxylamine compounds are important chemical intermediates in variousprocesses, especially in the microelectronic, pharmaceutical andagricultural industries. In the microelectronic industry hydroxylaminecompounds are used in printed circuit board fabrication, inmicroelectronic chip manufacture and in similar technology. For example,hydroxylamine compositions are extensively utilized as components ofso-called “stripper” solutions for removing developed photoresists suchas polyimide coatings from metal foils. In the pharmaceutical industryand in agricultural chemicals, the compounds are used as an intermediatein various chemical syntheses for commercially available products.

Utilization of hydroxylamine solutions for most of these purposesrequires an ultra-high purity form of the material. A major concern atevery stage in the manufacture of electronic components iscontamination. Control of contamination is critical to product quality.These requirements are particularly acute in the manufacture of veryhigh density circuitry and in ultra-high precision manufacturing.Frequently, solutions of hydroxylamine contain undesirable amounts ofanion and cation impurities particularly of various metal and metal ioncontaminations. In hydroxylamine photoresist stripper solutions suchimpurities even in trace amounts when introduced onto a semiconductorchip during its manufacture, tend to produce localized defects in thecrystalline structure which may then propagate to produce undesirablepittings and render the chip deficient or even useless for its intendedpurpose.

Often it is necessary to employ hydroxylamine in the form of a solutionof free base which is generally liberated from a hydroxylamine salt suchas hydroxylamine chloride or hydroxylamine sulfate by the action of anappropriate base such as ammonia, alkali metal hydroxides or analcoholate. Neutral or alkaline hydroxylamine solutions are unstable anddecompose exothermically by internal oxidation-reduction reaction toform ammonia, nitrogen, oxides of nitrogen and water.

The rate of decomposition is accelerated by a high pH and a highconcentration of catalytically active impurities. In order to avoiddecomposition of the hydroxylamine, a stabilizer is added to thesolution. Numerous stabilizers for hydroxylamines are already known.However, few stabilizers proposed to date have been of ultra high purityso as not to contaminate either the hydroxylamine solution per se or theion exchange resins used to purify the solution.

U.S. Pat. No. 4,166,842 to Tunick et al., which is incorporated hereinby reference, discloses the purification of hydroxylamine byliquid/liquid extraction.

U.S. Pat. No. 5,808,150 issued to Michelotti which is incorporatedherein by reference, discloses stabilizing aqueous, semi-aqueous ornon-aqueous solutions containing hydroxylamine or a partiallyneutralized hydroxylamine salt utilizing1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (“CDTA”) to minimizethe decomposition and provide stability over a longer period than knownstabilizers such as nitrilotriacetic acid and ethylene diaminetetraacetic acid. However, as commercially supplied for productionpurposes, CDTA contains a considerable amount of undesirable metals andmetal ions, which even at the low stabilizing amounts (i.e. 100 partsper million) imports an increase in the treated hydroxylamine solutionof the undesirable materials as to exceed the allowable limit of 10parts per billion required for an ultrahigh pure grade hydroxylaminecompound solution.

Clearly there is a need for an economical and relatively simple processto produce an ultrahigh purity CDTA particularly for use as a stabilizerfor hydroxylamine compound solutions, which will provide a high yield ofacceptable product for use in a wide variety of applications, especiallythose requiring high purity aqueous solutions of hydroxylamine.

This need is met by a process for preparing cis-ortrans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid which comprisesthe steps of

-   (a) neutralizing an aqueous solution of chloroacetic acid with a    nonmetal amino or hydroxide base;-   (b) reacting cis- or trans-1,2-diaminocyclohexane with the    neutralized chloroacetic acid of step (a) at an elevated    temperature;-   (c) treating the product from step (b) with a non-metal amino or    hydroxide base;-   (d) treating the resulting product of step (c) with acid and then-   (e) recovering the product formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The synthesis of cis- ortrans-1,2-diamino-cyclo-hexane-N,N,N′,N′-tetraacetic acid is a multistage process carried out in an aqueous medium, at least using deionizedwater but preferably distilled water. The initial step involves aneutralization reaction involving chloroacetic acid and a non-metalamine or hydroxide base solution. The chloroacetic acid is dissolved inwater in a concentration of about 20–70 weight percent and preferablyabout 30 weight percent and the temperature is lowered to 0° C. Aboutone-half of the neutralizing agent is added at this temperature in theform of a 10 weight percent solution of the non-metal amino or hydroxidebase solution to begin forming a chloroacetic acid-nonmetal ioniccomplex maintaining the temperature below 10° C. Cis- ortrans-1,2-diaminocyclohexane is added and the reaction mixture is heatedslowly. Using cis- or trans-1,2-diaminocyclohexane determines wethercis- or trans-CDTA will be produced. The stereoisomerism remainsunchanged. When the temperature reaches about 20° C. the other halfportion of the neutralizing agent is added dropwise while the heatingcontinues slowly to about 75° C.–80° C. Upon completion of the additionof the neutralizing agent, the reaction is stirred and heated up toabout, but not to exceed 100° C. for one hour. After the reaction iscomplete, the mixture is cooled and filtered for example using anaspirator filter to separate any formed crystals. The filtrate is slowlyacidified with concentrated hydrochloric acid. At about pH 3 aprecipitate will begin to form as crystals in the filtrate. The filtrateis then stirred, typically for 5 to 10 minutes. After the stirringperiod more hydrochloric acid is added dropwise until pH 2 is reached.The stirring is continued, typically for another 5 to 10 minutes, andthe filtrate is filtered and the CDTA crystals are recovered. Constantstirring and slow addition of the hydrochloric acid are critical toprovide a maximum yield. The final step in the synthesis involves arecrystallization in which a small portion of the CDTA prepared, asdescribed above, are dissolved in deionized water and sufficient amountof non-metal base solution is added until the crystals are dissolved inthe solution (at about pH 6–7). Dilute hydrochloric acid is addeddropwise slowly until the CDTA precipitated (about pH 4). The filtratewas also treated with diluted hydrochloric acid and a precipitate formed(about pH 2). All the precipitates may be collected for furtherprocessing.

The synthesis of 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acidaccording to the present invention is a multi-stage process carried outin an aqueous medium and the following equations show the reactions inthe various stages, with TMAOH being used as an example of a base in thefirst step and 30% NH₄OH being used as an example of a base in thesecond step:

-   TMA: trimethylammonium-   TMAOH=trimethylammonium hydroxide-   Wherein R is CH₂COOTMA and R¹ is CH₂COOH

A recrystallization process follows the above synthesis schemes toremove substantially any traces of the unwanted metals and metal ions.As described above, the process involves dissolving the CDTA indeionized water adding a non-metallic amino or hydroxide base to a pH of6–7, and precipitating the CDTA by the slow addition of dilutedhydrochloric acid to pH 4. After the precipitate forms the slow additionof diluted hydrochloric acid may continue until a pH 2 is reached. TheCDTA produced is of an ultra-high purity grade.

Non-metal amino or hydroxide bases are used for dissolving the free acidform of CDTA for the synthesis or for the recrystallization step. Forthe synthesis procedure the non-metal amino or hydroxide bases must beused in step (1) and (2). They need not be the same caustic. Forexample, trimethylammonium hydroxide is used in step (1) and ammoniumhydroxide in step (2).

Suitable non-metal amino or hydroxide bases useful in the CDTA synthesisare represented by the following formulae:NH₄OHR_(X)NH_(Y) ⁺OH⁻where: R=alkyl; x=1–4; y=0–3; x+y=4R_(X)NH_(Y)where: R=alkyl or alkanol; x=1–3; y=0–2; x+y=3(NH₄)_(X)H_(Y)PO₄where: x=1–3; y=0–2; x+y=3(R_(X)NH_(Y)) acetatewhere: R=alkyl; x=0–4; y=0–4; x=y=4

Examples of suitable bases are sodium hydroxide, tetraalkyl ammoniumhydroxide solutions, eg. tetramethyl ammonium hydroxide solution,tetraethylammonium hydroxide, alkanolamines such as monoethanolamine,isopropylamines, diethanolamine, 2-amino-1-propanol;2-amino-2-ethoxypropanol, ammonium hydroxide, inter alia. When usingammonium hydroxide the solutions should be freshly made and usedpreferably within 6 hours, since after about six hours storage thesolution starts to lose concentration, and at 24 hours deteriorationbecomes extensive.

Typically as an article of commerce CDTA as supplied contains 1000–5000ppm of unwanted metal or metal ions. Thus, by adding a conventionalamount of stabilizer about 100 ppm to the hydroxylamine solution theunwanted metal or metal ions would range from 100 to 500 ppb. This isclearly unacceptable for the stabilization of ultra-high purity gradehydroxylamine solutions, typically electronics grade where all theundesirable metals must be no more than 10 ppb.

The metals which play havoc in the production of high precisionelectronic components include alkali, alkaline earth metals andtransition metals and ions thereof. Specific examples of commonlyencountered unwanted metals and the corresponding ions includealuminium, calcium, chromium, cobalt, copper, iron, magnesium,potassium, and sodium.

The amount of stabilizer to be used to stabilize the hydroxylamine orthe at least partially neutralized hydroxylamine salt solution rangesfrom about 0.001 to about 0.1 percent by weight of composition.Preferably, the amount of stabilizer ranges from about 0.01 to about 0.5percent (100 to 500 ppm) same basis. The aqueous solutions of freehydroxylamine, i.e., fully neutralized salt, can be produced by thereaction of a salt of hydroxylamine (such as the hydrochloride, thenitrate, the acetate, the sulfate, etc.) with an alkali metal hydroxide(such as sodium hydroxide) or with ammonia. The concentration of thehydroxylamine salt is usually at least about 1 weight percent of theaqueous solution and can range up to about 70 percent or more, but isgenerally in the range form about 10 to 70 weight percent. It is best toadd the stabilizer to the hydroxylamine salt solution before itsneutralization with a base, but the stabilizer can also be added to theat least partially neutralized hydroxylamine salt solution and salt-freehydroxylamine solutions. The temperature during the addition beingadvantageously kept at from 5 degree(s) to about 40 degree(s) Celsius.The stabilized solutions should be stored at temperature <40 degree(s)Celsius, preferably <25 degree(s) Celsius.

It has been surprisingly found that the stabilizers of the inventionalso provide a caging effect similar in concept and practice to crownethers. This is due to the chemical and physical nature of thestabilizers of the present invention. When used in small amounts, thestabilizer acts as a host molecule and assumes a shape required for theformation of a complex or adduct to form a “cage” around and alkali ormultivalent alkali metal ion. This action prevents any redeposition ofor multivalent alkali metal ions onto a metal or non-metal wafersubstrate during stripping when used in a stripping composition. Forthis purpose, the stabilizers of the present invention can be used instripper formulations independent of hydroxylamine.

Hydroxylamine compounds can be stabilized by the ultra-high purity CDTAof the present invention include solutions of hydroxylamine or at leastpartially neutralized hydroxylamine salt and organic hydroxylamines.Hydroxylamine compounds may be represented by the formula:NR₃R₂OHwherein R₃ and R₂ are independently hydrogen or hydrocarbyl groupscontaining 1 to about 6 carbon atoms, and preferably R₃ and R₂ areindependently hydrogen or hydrocarbyl groups containing 1 to about 3carbon atoms.

Specific examples of R₂ an R₃ include hydrogen, and alkyl groups such asmethyl, ethyl, propyl, including isopropyl, butyl, etc. In embodimentswhere R₂ and R₃ are hydrogen, the hydroxylamine compound ishydroxylamine. In embodiment where at least one R₂ and R₃ is hydrocarbylgroup, the hydroxylamine compound is an organic hydroxylamine. The term“hydrocarbyl” is used herein to include hydrocarbyl as well assubstantially hydrocarbyl which means that non-hydrocarbyl substituentsdo not effect the hydrocarbyl substituents characteristics orproperties. Examples of organic hydroxylamines includemethylhydroxylamine, isopropylhydroxylamine and diethylhydroxylamine.

The following examples are set forth for purposes of illustration onlyand are not to be construed as limitations on the present inventionexcept as set forth in the appended claims. All parts and percentagesare by weight unless otherwise specified.

EXAMPLE 1

Into a vessel equipped with parts to accommodate a thermometer, acondensing column with a reflex cap, and a graduated liquid droppingcolumn with a stopcock were charged 85 g of chloroacetic acid anddissolved in 200 g of deionized (DI) water. The solution was cooled to0° C. and 135 g of 10% aqueous solution of Tetramethylammonium hydroxidewere added to neutralize the acid. During the neutralization thetemperature did not exceed 10° C. 26 g of 1,2-diaminocyclohexane wereadded and the reaction mixture was stirred for 1 hour at 100° C. andthen cooled to room temperature. The product was acidified slowly with100 g of concentrated hydrochloric acid to pH 3 with cloudy solutionformation. The cloudy solution was stirred for about 5 to 10 minutes.Additional concentrated hydrochloric acid was slowly added dropwiseuntil a pH 2 was reached and a precipitate was formed. The product wasfiltered and 1,2-diaminocyclohexane tetraacetic acid crystals wererecovered.

A portion (39.9 g) of the CDTA crystals was dissolved in another vesselin 100 ml, of DI water to which was added while stirring constantly 30%aqueous ammonium hydroxide (freshly made) until all the CDTA crystalsdissolved to form a clear solution at a pH 6 to 10. A diluted 18.5%hydrochloric acid was added slowly dropwise until a pH 4 was reachedwhere the CDTA begins to recrystallize into a cloudy solution. Themixture was stirred for about 5 to 10 minutes. Again diluted to 5%hydrochloric acid was added slowly dropwise until a pH 2 was reached ancomplete crystallization occurs. The mixture was filtered and the CDTArecovered.

The use of an ion exchange process for purifying hydroxylamine is wellknow. The following example shows the use of the CDTA of the presentinvention to stabilize an ultra-high purity grade hydroxylamine purifiedby an ion exchange method.

EXAMPLE 2

Into a 1 inch diameter glass column containing a stopcock was added 25ml of Purolite CT-151 cation exchange resin. The column was flushed with1 liter of DI water. The resin was then flushed with 1000 ml of 10%hydrochlorid acid. The column was tested by inductively coupled plasma(ICP) analysis to determine if all undesirable cations are removed. Thecolumn was then flushed with DI water until the chloride ion level was<0.5 ppm.

A 5% hydroxylamine solution was poured through the column to convert theacid groups to the amino salt and there was a mild exothermic reaction.After the isotherm was complete, a 50% hydroxylamine solution was passedthrough the column.

A glass column was prepared with Purolite anion exchange resin A-400similar to Part. I. 1000 ml of 8% KOH were passed through the column andthe column was then flushed with 2 liters of DI water until the K+analysis by ICP was <5 ppb. The 50% hydroxylamine solution processed wasthen passed through the anion exchange resin. The resulting solution wasstabilized with 0.5% by weight of1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid. The resultingsolution could be used in the preparation of a photoresist strippingcomposition having a metal and metal ion content of less than 10 ppb.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

1. A process for preparing cis- ortrans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid which comprisesthe steps of (a) neutralizing an aqueous solution of chloroacetic acidwith a non-metal amino or hydroxy base; (b) reacting cis- ortrans-1,2-diaminocyclohexane with a non-metal amino on hydroxy base; (c)treating the product from step (b) with a dilute solution of sodiumhydroxide; (d) treating the resulting product of step (c) with acid andthen (e) recovering the product formed.
 2. The process of claim 1wherein step (a) is conducted at a temperature not greater than 10° C.3. The process of claim 2 wherein the reaction of step (b) is at atemperature 75°–80° C.
 4. The process of claim 3, comprising the stepsof: (a) neutralizing chloroacetic acid in an aqueous medium with anon-metal amino or hydroxy base compound at a temperature of less than10° C.; (b) reacting said neutralized chloroacetic acid with1,2-diaminohexane at a temperature of less than 80° C.; (c) adding anon-metal amino or hydroxy base to complete neutralization so as to forman aqueous mixture; (d) heating the aqueous mixture to a temperature ofless than 100° C.; (e) filtering the mixture from (d); (f) treating theaqueous filtrate with hydrochloric acid until a precipitate forms; (g)filtering the aqueous filtrate; and then (h) recovering1,2-diaminocyclohexanetetraacetic acid and optionally redissolving said1,2-diaminocyclohexanetetraacetic acid in an aqueous solution andrepeating step (c).
 5. The process of claim 1 wherein the non-metalamino or hydroxy base is selected from the group consisting of sodiumhydroxide, tetramethyl ammonium hydroxide, tetraethylammonium hydroxide,monoethanolamine, isopropylamine, diethanolamine, 2-amino-1-propanol,2-amino-2-ethoxy propanol and mixtures thereof.
 6. The process of claim1 wherein the non-metal amino or hydroxy base in step (a) is differentfrom that used in step (c).
 7. The process of claim 1 wherein thenon-metal amino at hydroxy base in step (a) is tetramethylammoniumhydroxide and in step (b) ammonium hydroxide.
 8. The process of claim 1wherein sodium hydroxide is used as hydroxy base in steps (a) and (c).9. The process of claim 3 wherein the non-metal amino or hydroxy base isselected from the group consisting of sodium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, monoethanolamine,isopropylamine, diethanolamine, 2-amino-1-propanol, 2-amino-2-ethoxypropanol and mixtures thereof.
 10. The process of claim 3 wherein thenon-metal amino or hydroxy base in step (a) is different from that usedin step (c).
 11. The process of claim 3 wherein the non-metal amino orhydroxy base in step (a) is tetramethylammonium hydroxide and in step(b) ammonium hydroxide.
 12. The process of claim 3 wherein sodiumhydroxide is used as hydroxy base in steps (a) and (c).
 13. A processfor preparing cis- or trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraaceticacid which comprises the steps of (a) neutralizing chloroacetic acid inan aqueous medium with a non-metal amino or hydroxy base compound at atemperature of less than 10° C.; (b) reacting said neutralizedchloroacetic acid with 1,2-diaminohexane at a temperature of less than80° C.; (c) adding a non-metal amino or hydroxy base to completeneutralization so as to form an aqueous mixture; (d) heating the aqueousmixture to a temperature of less than 100° C.; (e) filtering the mixturefrom (d); (f) treating the aqueous filtrate with hydrochloric acid untila precipitate forms; (g) filtering the aqueous filtrate; and then (h)recovering 1,2-diaminocyclohexanetetraacetic acid and optionallyredissolving said 1,2-diaminocyclohexanetetraacetic acid in an aqueoussolution and repeating steps (c) to (g), wherein sodium hydroxide isused as hydroxy base in steps (a) and (c).